The Pediatric Oncology Fellowship Program at the University of Colorado Health Sciences Center (UCHSC) and Denver Children's Hospital, has a distinguished history spanning over 30 years. In 1993, substantial new resources were dedicated to the development of this Program, leading to the establishment of a Bone Marrow Transplant unit, Neuro-oncology service, and a core group of basic scientists. In addition, the fellowship program was expanded and fellows were given the opportunity to perform research in any laboratory in the UCHSC system. The training program was funded in 2000 with this T32 grant, and the current submission is the competing renewal of this support. Presently 24 Training Faculty represent a broad range of scientific disciplines including cell cycle control and signaling, transcriptional regulation and splicing, virology, and immunology. These diverse disciplines and approaches are unified by use of molecular approaches to address fundamental biological questions, and by their applicability to problems in oncology research. Because of the breadth of the clinical experience, the fine clinical reputation of the Children's Hospital, and the new research opportunities available, fellowship candidates since 1993 have consistently increased in quality and dedication to an academic career. Indeed, 15 of 19 graduates since 1993 are now in academic faculty positions. The minimal fellowship duration is three years, with the first year exclusively clinical training. Currently there are 11 fellows in the Program, all of whom have previously completed their Pediatric residencies, with 8 currently in research training beyond their first clinical fellowship year. This proposal seeks funding for those fellows who elect to pursue research related to Pediatric Oncology in the second and subsequent years of the fellowship. Both history and recent developments thus mark this training program as one of the best in the nation.